CiCi Bellis is the second American girl in three years to clinch the year-end No. 1 junior ranking. AP Photo/Darron Cummings

The 15-year-old Bellis was the sensation of this year's US Open, stunning Australian Open finalist Dominika Cibulkova in the first round to become the youngest player to win a match at that Grand Slam tournament since Anna Kournikova in 1996.

Bellis earned her spot in the main draw by winning the USTA Girls' 18s National Championship, the youngest to do so since Lindsay Davenport in 1991.

She's the second American girl in three years to rank No. 1 at year's end. Before Taylor Townsend accomplished the feat in 2012, it had been three decades since an American girl held that distinction.

Bellis clinched the ranking with a quarterfinal victory at the Orange Bowl Junior Championships on Friday.